1. Field of the Invention
This invention is in the field of shipping and storing equipment. Specifically it relates to collapsible stackable shipping and storing containers.
2. Background Information
This invention relates to a stackable container which has the ability to be a "knock down" container. By "knock down", it is meant that the container can be taken apart, into several different pieces. However, the container can still be easily reassembled. This ability gives the container the important feature of being shipped in pieces which greatly reduces freight costs for unassembled containers.
The problem of high freight costs for shipping an empty or newly completed stacking containers has existed for many years. Units have been previously manufactured to take advantage of the knock down feature, however none of them have been able to meet the Rack Manufacturers Institute standards for dynamic loading. Basically this means that when assembled, the knock down containers were either too shaky or could not support enough weight to be useful to industry.
One clear example of the problem is displayed in U.S. Pat. No. 3,762,343 to Thacker. As part of the Thacker disclosure and claims, a knock down stackable container is discussed. The Thacker patent teaches that to make a knock down unit, short lengths of corner columns are welded to the deck members and the top frame. Upright posts are designed with integral, inwardly projections which extend from the inside the upright posts into the deck and top frame corner columns. This structure, when constructed of tubing similar to the balance of the container, does not provide the necessary structural integrity. As a result, the Thacker knock down container is not used by industry. A continued search exists for a knock down container which meets the Rack Manufacturers Institute (RMI) standards (RMI Paragraph 8.2.2 "Stacked Load Capacity Test") and can withstand the use in industry.
The principle problem in producing a knock down container which meets the RMI standards is column loading. There are two types of stresses which affect the columns, axial and bending. The axial stresses are developed from loaded containers being stacked directly above one another, however, these stresses are minor. The majority of the stress is caused by bending moments on the columns. The columns must withstand both manufacturing misalignments and, more severely, a required RMI 3% grade design specification. Visually, this means that a lower most loaded knock down container must be able to withstand being placed at a 3% grade with 3 or 4 fully loaded knock down containers placed on top of the first container. The standard is important because it insures integrity of stackable containers by assuring that the lower most container will not collapse due to the demanding stresses developed from any movement of loads which are supported by and above the lower most unit. A 3% grade produces a bending force which current knock down container designs cannot withstand.
With currently designed knock down containers the bending forces have generally buckled the connection joint between the container top and the column or, more typically, between the container deck and the column. This means that in service the currently designed knock down containers actually collapse at the joints. Thus, it this connection joint that has been reinvented.
In view of the above problems, it a principle object of this invention to provide a knock down stackable container which meets the RMI standards. It is a further object of this invention to provide a knock down stackable container with a connection point between the top of the container and the column and between the deck of the container and the column which resists bending forces.
In the most preferred embodiment and end nesting stackable container is used and not only a stacking container. An end nesting stackable container is one which fits inside other like containers yet also stacks one on top of another. This combination of features allows for ease in shipping and storing material held in the containers by use of the stacking feature. Also the containers may be cost effectively shipped empty by use of the nesting feature because many empty nested containers take only the space of one filled container. Thus, the knock down end nesting stackable container would provide the greatest flexibility in shipping and storing material known to date.